Upgrading my pc cpu or video card which one is more better i play games on it?

Graphics Card is the main thing for any game.

The higher the resolution you play in the more the CPU will be pushed but if you have a standard res, anything up to 1680x1050, all you will need for any game is a top of the line Graphics Card, try a 3870 512MB DDR4 or 8800GTS 512MB DDR3

the video card allows you to play games better. a cpu allows you to see the game but does not contribute at all to how fast it loads. if you have a good cpu but not a decent video card it is unlikely to work properly.

graphic cards contribute more to better quality graphics in games,

however your graphic card can only do so much which is limited by your processor.

I would probably go for a new graphic card first before processor.

video card, get the best you can afford. you can also add RAM and upgrade to a HDD with a bigger cache...

depends what do you have now.how much want you spent?

for 500$ you can get good parts.